1. Field of the Invention
The present invention relates to telecommunications cables. More particularly, the present invention relates to a telecommunication cable having strength members adjacent to or embedded in a protective jacket made from a polymeric material having an adhesion promoter blended therein.
2. Description of the Prior Art
Telecommunications cables containing optical fiber cables have been used by the telecommunications industry for a number of years to transmit information at very high rates over long distances. Because the optical fiber transmission elements are delicate, the telecommunications cables are provided with members which are designed to protect the optical fibers. For example, in a typical optical fiber telecommunications cable, one or more optical fibers are disposed in a buffer tube which provides some protection against abrasion, as well as outside tensile and compressive forces. In a basic central tube design, a single buffer tube may be surrounded by an armor layer made from aramid yarns, water blocking tapes, metallic sheaths or some combination of such materials. The armor layer is typically surrounded by an outer protective sheath made from a polyolfin material such as medium density polyethylene (MDPE) or high density polyethylene (HDPE). To provide additional compressive and tensile strength to the cable, the outer protective jacket may be extruded over strength members made from composite materials containing glass reinforced fibers or steel so that such members become embedded in the outer protective jacket.
In some cables, copolymer adhesion promoters, such as ethylene-acrylic acid (EAA) are applied as a coating on composite strength members to promote adhesion between the strength members and the jacket extruded thereover. Alternatively, steel armor may be precoated with a copolymer material which promotes adhesion. Such strength members are marketed by t he Dow Chemical company under the ZETABON trademark. The jacket material is then extruded over this copolymer coated steel armor. Copolymer coatings, however, have the disadvantage that adhesion cannot be controlled during cable manufacturing.
Control of bonding is desirable in fiber optic cables to allow a combination of mechanical integrity and ease of cable access. If adhesion between the jacket and strength members or jacket is too low, debonding may occur during handling or installation. If jacket debonding occurs, the cable may show numerous mechanical or other problems. For example, if the strength members become debonded from the jacket pistoning of the strength members may be seen with temperature variation due to the different coefficient of thermal expansion (CTE) values for the different materials. If t he jacket and strength members do not remain coupled, low temperature cable contraction may be too high and attenuation may result. Additionally, debonding can result in water penetration failures in the cable. If the level of adhesion is too high, especially between steel armor ad the jacket, cable access may be difficult for splicing operations thereby increasing the effective time for cable access and splicing.
To control bonding, some have applied hot melt or other types of adhesives to the strength members or armor prior to the extrusion of the jacket material over the strength member or armor. These materials have become necessary to obtain the desired level of mechanical coupling or bonding between the jacket and the strength members or armor. However, the application of these materials to the strength member or armor during the cable manufacturing process increases the cost of manufacturing by adding another step to the manufacturing process.
Accordingly, what is needed is a mechanism to provide and control the adhesion between embedded elongated strength members and the protective jacket material during the jacketing process without significantly adding to the manufacturing cost of the cable. The present invention is intended to provide such a mechanism.